Navigation state persistence in React Native - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the hook that helps save navigation state.

React Native

import { [1] } from '@react-navigation/native';

Drag options to blanks, or click blank then click option'

AuseNavigationContainerRef

BuseNavigationPersistence

CuseNavigationStatePersistence

DuseNavigationState

Attempts:

3 left

💡 Hint

Common Mistakes

Using a hook that does not exist in the library.

Confusing navigation state hooks with navigation container refs.

The hook useNavigationContainerRef is used to create a ref to the navigation container, which helps in persisting navigation state.

2fill in blank

medium

Complete the code to load the saved navigation state from async storage.

React Native

const loadState = async () => {
  const savedState = await AsyncStorage.[1]('NAVIGATION_STATE');
  if (savedState) {
    setInitialState(JSON.parse(savedState));
  }
};

Drag options to blanks, or click blank then click option'

AsetItem

BgetItem

CremoveItem

Dclear

Attempts:

3 left

💡 Hint

Common Mistakes

Using setItem instead of getItem to read data.

Trying to remove or clear storage instead of reading.

AsyncStorage.getItem is used to retrieve a saved value by key.

3fill in blank

hard

Fix the error in saving the navigation state when it changes.

React Native

const onStateChange = (state) => {
  AsyncStorage.[1]('NAVIGATION_STATE', JSON.stringify(state));
};

Drag options to blanks, or click blank then click option'

AgetItem

BmergeItem

CremoveItem

DsetItem

Attempts:

3 left

💡 Hint

Common Mistakes

Using getItem instead of setItem to save data.

Not converting state to a string before saving.

To save data to AsyncStorage, use setItem with a key and string value.

4fill in blank

hard

Fill both blanks to correctly initialize navigation container with persistence.

React Native

const navigationRef = [1]();

<NavigationContainer
  ref={navigationRef}
  initialState={initialState}
  onStateChange={onStateChange}
>[2]</NavigationContainer>

Drag options to blanks, or click blank then click option'

AuseNavigationContainerRef

BuseState

C<StackNavigator />

D<TabNavigator />

Attempts:

3 left

💡 Hint

Common Mistakes

Using useState instead of useNavigationContainerRef for the ref.

Placing no navigator or wrong navigator inside NavigationContainer.

useNavigationContainerRef creates the ref for navigation container. The StackNavigator component is placed inside NavigationContainer to define screens.

5fill in blank

hard

Fill all three blanks to complete the async effect that loads saved navigation state on app start.

React Native

useEffect(() => {
  const restoreState = async () => {
    const savedState = await AsyncStorage.[1]('NAVIGATION_STATE');
    if (savedState) {
      setInitialState(JSON.[2](savedState));
    }
    setIsReady(true);
  };
  if (!isReady) {
    restoreState();
  }
}, [[3]]);

Drag options to blanks, or click blank then click option'

AgetItem

Bparse

CisReady

DsetItem

Attempts:

3 left

💡 Hint

Common Mistakes

Using setItem instead of getItem to read data.

Using JSON.stringify instead of JSON.parse to convert data.

Leaving dependency array empty causing multiple runs.

getItem reads the saved state, JSON.parse converts it back to an object, and isReady is the dependency to run effect only once.

Practice

1. What is the main purpose of navigation state persistence in a React Native app?

easy

A. To change the app's theme based on user preference

B. To speed up the app's loading time by caching images

C. To save the user's current screen so they return to it after closing the app

D. To reset the app to the home screen every time it opens

Solution

1. Step 1: Understand navigation state persistence

   Navigation state persistence means saving where the user is in the app so they can continue from the same place later.

2. Step 2: Identify the correct purpose

   Only To save the user's current screen so they return to it after closing the app describes saving the current screen to restore it after app restart.

3. Final Answer:

   To save the user's current screen so they return to it after closing the app -> Option C

4. Quick Check:

   Navigation state persistence = save current screen [OK]

Hint: Remember: persistence means saving state for later use [OK]

Common Mistakes:

• Confusing navigation state with app theme or cache
• Thinking it resets app screens instead of saving them

2. Which of the following is the correct way to use NavigationContainer for state persistence?

easy

A.

B.

C.

D.

Solution

1. Step 1: Recall NavigationContainer props for persistence

   The correct props are initialState to set saved state and onStateChange to save new state.

2. Step 2: Match options with correct props

   Only uses initialState and onStateChange correctly.

3. Final Answer:

   <NavigationContainer initialState={savedState} onStateChange={saveState}> -> Option D

4. Quick Check:

   Use initialState and onStateChange props [OK]

Hint: Look for exact prop names: initialState and onStateChange [OK]

Common Mistakes:

• Using wrong prop names like state or onChange
• Swapping savedState and saveState variables

3. Given this code snippet, what will happen after the user navigates to 'Profile' and the app restarts?

const [initialState, setInitialState] = React.useState();
React.useEffect(() => {
  AsyncStorage.getItem('NAV_STATE').then(state => {
    if(state) setInitialState(JSON.parse(state));
  });
}, []);

 AsyncStorage.setItem('NAV_STATE', JSON.stringify(state))}
>
  {/* screens */}
;

medium

A. The app opens on the default initial screen ignoring saved state

B. The app opens on the 'Profile' screen automatically

C. The app crashes due to missing navigation state

D. The app opens on a blank screen

Solution

1. Step 1: Understand AsyncStorage usage

   The code loads saved navigation state from AsyncStorage and sets it as initialState.

2. Step 2: Effect of initialState on NavigationContainer

   Passing initialState restores the last screen, so the app opens on 'Profile' after restart.

3. Final Answer:

   The app opens on the 'Profile' screen automatically -> Option B

4. Quick Check:

   Saved state restores last screen [OK]

Hint: Saved state in initialState restores last screen [OK]

Common Mistakes:

• Assuming app ignores saved state and resets
• Thinking missing state causes crash

4. Identify the bug in this code that tries to persist navigation state:

const [navState, setNavState] = React.useState();

React.useEffect(() => {
  AsyncStorage.getItem('NAV_STATE').then(state => {
    setNavState(state);
  });
}, []);

 AsyncStorage.setItem('NAV_STATE', JSON.stringify(state))}
>
  {/* screens */}
;

medium

A. The saved state is not parsed from JSON before setting navState

B. The onStateChange callback should not stringify the state

C. initialState should be set to null instead of undefined

D. AsyncStorage.getItem should be called inside onStateChange

Solution

1. Step 1: Check AsyncStorage.getItem usage

   AsyncStorage.getItem returns a JSON string, so it must be parsed before use.

2. Step 2: Identify missing JSON.parse

   The code sets navState directly to the string, causing navigation to fail.

3. Final Answer:

   The saved state is not parsed from JSON before setting navState -> Option A

4. Quick Check:

   Parse JSON before setting state [OK]

Hint: Always parse JSON from AsyncStorage before using [OK]

Common Mistakes:

• Forgetting JSON.parse on saved state
• Misusing onStateChange callback

5. You want to persist navigation state but only save it after the user has navigated at least once. Which approach correctly implements this behavior?

hard

A. Use a ref to track if navigation happened, then save state in onStateChange only if true

B. Save state immediately on app start inside useEffect

C. Call AsyncStorage.clear() before saving state to avoid duplicates

D. Set initialState to null and never update it

Solution

1. Step 1: Understand conditional saving need

   We want to save navigation state only after user navigates once, so we track navigation occurrence.

2. Step 2: Use a ref to track navigation

   A ref can store a boolean flag that updates on first navigation, then onStateChange saves state only if true.

3. Step 3: Evaluate other options

   Save state immediately on app start inside useEffect saves immediately, ignoring condition; C clears storage unnecessarily; D disables persistence.

4. Final Answer:

   Use a ref to track if navigation happened, then save state in onStateChange only if true -> Option A

5. Quick Check:

   Track navigation with ref before saving state [OK]

Hint: Use a ref flag to save state only after first navigation [OK]

Common Mistakes:

• Saving state too early before navigation
• Clearing storage unnecessarily
• Ignoring initialState updates